Humans don’t have a defined mating season like deer or wolves. Here’s how evolution blended biology, culture and social life into year-round intimacy.

Geneticists have a better understanding of how prehistoric pairings unfolded, with new research suggesting they were mostly between male Neanderthals and female humans.

Long ago, Neanderthals and modern humans interbred. But among Neanderthals, their modern human blood came mostly from their ...